Dr. Sibley and coworkers have expressed both dihydrofolate reductase and dihydropteroate synthase from Plasmodium falciparum in the budding yeast, Saccharomyces cerevisiae and shown that one can study the parasite enzymes in this simple system. When completed their experiments will provide a detailed understanding of the mutations that modify function of the Pf-DHFR and Pf-DHPS enzymes or sensitivity of the enzymes to antifolate drugs.